Ecology of the Burgess Shale
Aim
We are going to investigate the ecology of an ancient community of marine animals
by using information from the famous Burgess Shale fossil site in Canada. If you
wish, you can use Microsoft Excel to analyse the data and answer the questions.
Introduction
The Burgess Shale is a 515 million year old fossil site located high up in the Rocky
Mountains of British Columbia, Canada. Many thousands of primitive animal fossils
have been found there making it one of the best places to hunt for fossils in the world.
When an animal is fossilized, usually only the hard parts survive such as the shell or
bones. What makes the Burgess Shale so special is that it also preserves the soft parts
such as muscle tissue. Because all members of this fossil community are preserved we
can learn about its food chain.
All ecosystems are made up of a web of relationships with primary producers being
eaten by primary consumers, which in turned at predated by secondary consumers.
Energy is lost at each level in the food chain. To understand the pattern of energy
flow in an ecosystem is important to know the number of animals at level of the food
web. We are going to find out this information for the Burgess Shale ecosystem by
doing a simple calculation.
Food Chain of the Burgess Shale
On the handout you are given a table showing the 25 most common animal species
found in the Burgess Shale. For each you are told: (1) whether that species had any
hard parts, or whether it was entirely soft-bodied, (2) the number of specimens of that
species that have been found, (3) the average length of the species, and (4) the way in
which it fed.
In the table, the following abbreviations are used for mode of feeding:
S, Suspension Feeder, meaning that the animal captured particles of organic material
floating through the water a bit like shellfish feed today (a primary consumer)
D, Deposit Feeder, meaning that the animal ate any dead or decaying organic material
that was lying on or within the muddy seabed, a bit like a worm feeds today (a
primary consumer)
P, Predatory Feeder, meaning that the animal killed and ate other animals a bit like
shark or octopus feed today (a secondary consumer)
The primary producers in the ecosystem are green algae but are not listed in the table
Calculation
To learn more about the food chain of the Burgess Shale ecosystem, use the
information in the table to draw two bar charts that show the percentage of animals in
each of the three feeding categories.
In the first bar chart calculate the percentages based on the number of individual
specimens in each feeding category. Note there are a total of 35,497 individual
represented in the table.
In the second bar chart re-calculate the percentages taking into account the different
size of organisms. You can do this by multiplying the number of individuals of each
species by the average length of that species. Then add together the results for each
species in each feeding group.
E.g. Feeding group 1 = (no. of Species A x length) + (no. of Species B x length) + etc
The table is also available as an Excel spreadsheet. Why not try using the simple
maths functions to do the calculations and plot your charts using the Chart function?
Questions
1. On your first bar chart, how many secondary consumers (predators) are there
relative to primary consumers (deposit and suspension feeders)? Can you
think of a reason for this pattern?
2. Compare your two bar charts. How does the relative proportion of secondary
consumers (predator) differ when size is taken into account? What does this
tell you about the predators?
3. If the Burgess Shale was a normal fossil site where only hard parts are
preserved, how would this change your understanding of the ecosystem?
4. Do you think that the Burgess Shale fossil site is representative of what marine
life was like 515 million years ago?
Image: Arthropleura (top left) captures a trilobite
Table: Information about the Burgess Shale fossils
Name of
animal
Any hard
parts?
Number of
individuals
Length
(mm)
Feeding
category
Aysheaia
No
20
60
P
Branchiocaris
No
4
80
P
Burgessia
No
2140
30
D
Canadaspis
No
4676
55
D
Helmetia
No
12
200
S
Marrella
No
14956
12
D
Naraoia
Yes
128
30
P
Odaraia
No
24
150
P
Olenoides
Yes
84
70
P
Polychaete
No
9200
2
S
Sidneyia
No
176
120
P
Waptia
No
1020
75
D
Yohoia
No
384
15
P
Burgessochaeta
No
376
30
P
Canadia
No
188
30
P
Ottoia
No
1480
80
P
Selkirkia
No
188
35
P
Eiffelia
No
16
20
S
Priania
No
128
25
S
Dictyonina
No
12
8
S
Pikaia
No
60
40
S
Dinomischus
No
3
20
S
Hallucigenia
No
40
20
P
Opabinia
No
28
50
P
Wiwaxia
No
136
30
P
Worked answer
Table for Bar Chart 1
Predatory feeder
Deposit feeder
Suspension feeder
Total
Number of Individuals
3,256
22,792
9,431
35,479
Percentage
9.18
64.24
26.58
100.00
Individuals x Length
185,820
577,352
192,476
955,648
Percentage
19.44
60.41
20.14
100.00
Table for Bar Chart 2
Predatory feeder
Deposit feeder
Suspension feeder
Total
Answers
1. On your first bar chart, how many secondary consumers (predators) are there
relative to primary consumers (deposit and suspension feeders)? Can you
think of a reason for this pattern?
Secondary consumers (predators) make up 9.18% while primary consumers
make up 88.82% (deposit feeders 64.24%, suspension feeders 26.58%).
Energy is lost at each level in the food chain, so the ecosystem can support far
fewer predators than primary producers.
2. Compare your two bar charts. How does the relative proportion of secondary
consumers (predator) differ when size is taken into account? What does this
tell you about the predators?
Predators are twice as important when body size is taken into account, making
up 19.44% of the total. This is because predators, although small in numbers,
are generally much larger.
3. If the Burgess Shale was a normal fossil site where only hard parts are
preserved, how would this change your understanding of the ecosystem?
Yes, our understanding would be completely different! Only two species in
the table have hard parts, these being Naraoia and Olenoides so this is all
we’d know about.
4. Do you think that the Burgess Shale fossil site is representative of what marine
life was like 515 million years ago?
Yes, because it preserves soft-bodied organisms as well as those with hard
parts, it preserves a complete cross-section of life in that part of the ocean at
that time. Normal fossil sites by contrast are highly biased as they only
preserve the animals that have hard parts.